About IPv4 Subnet Calculator

Cisco wildcard mask, host range and quantity of hosts. Online and for free. The wildcard is the inverse netmask used for access control lists (ACL's) in Cisco routers.
This free online IPv4 subnet calculator also can be used as a teaching tool and presents the subnetting results as easy-to-understand binary values.
We can see two things: all host bits are zeroes in a network address, in a broadcast address they are all set.
First bits determine the class of your network from A to E. A, B and C are commonly used. Each class has a range of valid IP addresses.
Address Range of Class A - 1.0.0.1 to 126.255.255.254 (supports 16 million hosts on each of 127 networks).
Class B - 128.1.0.1 to 191.255.255.254 (65,000 hosts on each of 16,000 networks).
Class C - 192.0.1.1 to 223.255.254.254 (254 hosts on each of 2 million networks).
Class D - 224.0.0.0 to 239.255.255.255 (address range reserved for multicast groups).
Class E - 240.0.0.0 to 254.255.255.254 (reserved for future use, research and development purposes).